For coating materials for use in turbine blades and nozzle guide vane of jet engines and industrial gas turbines, conventionally, Al, Cr, Ni—Al, Pt—Al, MCrAlY are well known and actually utilized widely. However, when these coating materials are applied to a turbine blade made of an Ni-based superalloy and the turbine blade is used at high temperatures for a long period of time, interdiffusion of elements proceeds through the interface between the Ni-based superalloy and the coating material, and the interdiffusion of elements degrades the quality of material of the Ni-based superalloy, to generate such problems on material technology as lowering in strength and lowering in circumstance resistance property of the coating material that lead to lowering in the durability of the turbine blade itself. In particular, in these years, the gas temperature for jet engines and gas turbines is heightened, and, naturally, the temperature of the turbine blade rises, to accelerate further such diffusion phenomenon. In addition, high pressure turbine blades have a hollow construction for cooling, and, since reduction in the wall thickness is proceeding, the influence of the diffusion region constitutes a growing problem.
For the purpose of preventing the diffusion of elements through the substrate/coating interface, a diffusion barrier coating is examined (for example, see Patent Document 1). However, the diffusion barrier coating has a multilayer structure to complicate the coating process, and, in addition, since a substrate and a coating material are not in the thermodynamical equilibrium state, there is some limit of the effect as a natural result.
On the other hand, US 2004/0229075 (Patent Document 2), which has been published recently, discloses to decrease the diffusion of Al by coating of the γ+γ′ phase containing Pt having a lowered concentration of Al element being an element that diffuses farthest and generates a harmful phase by diffusion. However, in this instance also, since the substrate and the coating material are not in the thermodynamical equilibrium state, during the use at high temperatures for a long period of time, Pt and Al diffuse from the coating material toward the inside, and a strengthening element diffuses from the substrate toward the outside, to develop the degradation of material. Thus, the effect is restrictive.
Patent Document 1: U.S. Pat. No. 6,830,827
Patent Document 2: U.S. Patent Application No. 2004/0229075